WEDNESDAY, May 8, 2019 (HealthDay News) -- High levels of a protein linked with the brain disease chronic traumatic encephalopathy (CTE) were found in the cerebrospinal fluid of ex-athletes who suffered multiple concussions, Canadian researchers say.

The protein tau has been tied to CTE, a rare, degenerative brain disease believed to stem from repeated impacts to the head. People with CTE develop symptoms such as dementia, personality disorders or behavior problems.

This study included 22 former professional athletes, average age 56, with a history of multiple concussions. The men included 12 Canadian Football League players, nine hockey players and one snowboarder. They were compared to 12 people with Alzheimer's disease and five healthy people.

Researchers checked tau levels in the participants' cerebrospinal fluid, which surrounds the spine and brain.

Of the former athletes, 12 (54%) had high levels of tau. Their levels (averaging 349 picograms per milliliter) were higher than the healthy people (188 pg/ml), but lower than the Alzheimer's patients (857 pg/ml). A high level was considered anything above 300 pg/ml.

Men with high tau levels had lower scores on a test of thinking skills than those with normal tau, and brain scans showed that their white matter was not as healthy. White matter is composed of nerve fibers that send signals throughout the brain.

There was no difference in the number of concussions or the number of years played between athletes with normal and high tau levels.

The study was published online May 8 in the journal Neurology.

"The findings support the idea that multiple concussions or head impacts put some people at risk of developing neurodegeneration, which is the progressive loss of nerve cells, and possibly CTE, and this may be detected by measuring cerebrospinal fluid tau," said study author Dr. Maria Carmela Tartaglia.

She is an assistant professor of medicine at the University of Toronto.

"It also highlights the importance of finding a biomarker of CTE that can be measured while someone is alive, since currently a CTE diagnosis can only be determined in an autopsy, and not all players who suffered multiple concussions had elevated tau," Tartaglia said in a journal news release.